First, focus on conquering the other Mayan states so you can form Maya, then you can focus on reforming the Mayan religion. Do whatever you can to pass reforms as quickly as you can. The advantage of the Mayans over the Central Americans is that the Mayan religion has no Doomsday; so that's one less problem for you. Just focus on crushing the Central American countries and Mayan vassals that try to revolt against you. The most important reform is the Colonist one, especially if you start at a date earlier than 1444, however for Xiu and Cocomes, this isn't much of an option due to their late starting date. Having as much of the Americas colonized before the Europeans show up is your top priority after reforming the Mayan religion.